Internet Protocol Multimedia Subsystem (IMS) is an architectural framework for delivering Internet Protocol (IP) multimedia to mobile devices (e.g., smart phones, tablets, etc.) that are associated with users of the IMS network. An IMS core network (sometimes referred to as the “IMS core”, or the “Core Network (CN)”) permits wireless and wireline devices to access IP multimedia, messaging, and voice applications and services.
The IMS core is agnostic to the access technology that is used to connect mobile devices (commonly referred to as “user equipment (UE)”) to the IMS core network. In this manner, a user's mobile device can connect to the IMS network via any suitable radio access network (RAN) that is available to the mobile device. For example, a mobile device can connect to the IMS core via a 3rd Generation Partnership Project (3GPP) RAN, such a GSM/EDGE RAN (GERAN), a Universal Terrestrial RAN (UTRAN), or an evolved UTRAN (E-UTRAN). Accessing the IMS core through these types of 3GPP RANs typically involves communicating with the IMS core network through a cell site (cell tower). Alternatively, mobile devices can connect to the IMS core via a “non-3GPP” RAN, such as a Wi-Fi™ RAN, or another type of wireless local area network (WLAN) that is based on the Institute of Electrical and Electronics Engineers' (IEEE) 802.11 standards. Accessing the IMS core through a Wi-Fi access network typically involves communicating with the IMS core through a Wi-Fi Access Point (AP). Providing access to the IMS core through non-3GPP RANs has opened the door to recent advancements in IMS-based services, such as the introduction of Wi-Fi calling, which allows users to initiate and receive calls over an available Wi-Fi AP.
With respect to non-3GPP RANs, the 3GPP standard defines two types of access: trusted and untrusted. In general, a trusted RAN is a RAN that is operated by the IMS core operator, or by another trusted party to the IMS core operator (e.g., a contractor, an affiliate, an industry partner, etc.). By contrast, an untrusted RAN is a RAN that connects UE to the IMS core through a Wi-Fi AP and a public network, such as the Internet, which the IMS operator has no control over. For example, a mobile device may connect to the IMS core network through public hotspots, a subscriber's home Wi-Fi, corporate Wi-Fi, and so on.
When users access IMS-based services over an untrusted RAN, a wireless carrier is unable to ascertain the user's location. This is primarily due to the infrastructure of untrusted RANs. That is, wireless carriers (or cellular network operators) don't own the backhaul for untrusted RANs, and as a consequence, the transmissions from mobile devices are transmitted over an open and public network (e.g., the Internet) before the transmissions are received at the carrier-owned IMS core network. In the absence of location information for the untrusted RAN equipment (e.g., location of Wi-Fi APs), the carrier cannot ascertain the user's location. Considering that a transient user may carry his/her mobile device to any location/Wi-Fi AP where the user has security credentials to access an untrusted RAN, the user can obtain access to IMS-based services while the carrier does not know the subscriber's location.
There are many reasons why the carrier may need to know the current location of a user/subscriber. For example, federal regulations specify that a subscriber is to have a reasonable expectation that he/she can dial 911 and be routed to the correct (i.e., nearest) public safety answering point. There are also non-emergency short codes (e.g., poison control, 811—call before you dig, 311 city non-emergency, text to 911, etc.) that are routed to an appropriate long number based on location. Furthermore, the types of restrictions applied by carriers at the time of IMS service registration may vary by location of the subscriber. Without knowledge of the subscriber's current location, none of this is possible. Another example relates to billing subscribers at appropriate rates. That is, billing rates associated with use of IMS-based services (e.g., telephony services) can vary by the location of the subscriber when the services are used. Without knowledge of the subscriber's current location, billing at different rates based on location is not possible.